Elsevier

Journal of Dentistry

Volume 35, Issue 9, September 2007, Pages 701-711
Journal of Dentistry

Review
The role of manufacturers in reducing biofilms in dental chair waterlines

https://doi.org/10.1016/j.jdent.2007.05.003Get rights and content

Abstract

Objectives

This paper reviews how dental chair unit (DCU) manufacturers can contribute practically to resolving the problem of biofilm formation in dental unit waterlines (DUWs).

Study selection

The review concentrates on how novel developments and changes in a range of specific areas have, and might contribute to DUW biofilm control. These include (i) DCU engineering and design changes; (ii) improvements to DCU supply water quality; (iii) development of automated DUW treatment procedures that are effective at controlling biofilm in the long-term, safe for patients and dental staff, environmentally friendly and which do not exhibit adverse effects on DCU components after prolonged use.

Sources

The majority of the material contained in this review is based on, or supported by the peer-reviewed literature.

Data

The current consensus from the literature reveals that the emphasis on DUW biofilm and its control has focused on describing the problem and its control using a range of periodic and residual DUW treatment agents. Unfortunately, until recently, DCU manufacturers have provided very little specific guidance in this regard. Indeed, ensuring that DCUs provide good quality output water has generally been regarded to be the responsibility of dental practitioners. Some recent studies have shown that novel DCUs with integral semi-automated or automated DUW cleaning systems can effectively control DUW biofilm in the long-term. However, there are other potential DCU engineering and design changes that DCU manufacturers could undertake to further improve DUW biofilm control.

Conclusions

DCU manufacturers can significantly contribute to controlling the problem of DUW biofilm.

Introduction

Modern dental chair units (DCUs) are classified as medical devices under the EU Medical Devices Directive.1 According to this Directive, a medical device is “any instrument, apparatus, appliance, material or other article, whether used alone or in combination, including the software necessary for its proper application, intended by the manufacturer to be used for human beings for the purpose of diagnosis, prevention, monitoring, treatment or alleviation of disease”. Microbial contamination of a wide range of medical devices, such as anaesthetic equipment, laryngoscopes, endoscopes, gastroscopes, mechanical ventilators, resuscitation tubes, colonoscopes and catheters, has been recognised as an important cause of cross-contamination and cross-infection, especially in the hospital setting.2 Wet or moist sites or surfaces of medical devices have been particularly associated with cross-infection and cross-contamination because such areas are conducive to the growth of microbial biofilm. Because DCUs are used in the treatment of many patients throughout each day, microbial contamination of specific component parts is an important potential source of cross-infection.2 Of particular concern are parts of DCUs that come into direct contact with the patient's oral cavity, including dental unit handpieces, three-in-one air/water syringes and suction hoses. DCU output water is also of concern as a source of potential cross-infection as it comes directly from the DCU and enters the oral cavity of the patient during treatment.2 Furthermore, droplets and aerosols generated by DCU handpieces may be inhaled by patients and dental healthcare personnel.[3], [4], [5], [6]

DCUs consist of several complex, integrated equipment systems that are central to the practice of modern dentistry. These systems are designed to provide the instruments and services necessary for a diverse range of dental procedures.[6], [7], [8] DCUs use water to cool and irrigate a variety of DCU-supplied instruments and tooth surfaces during dental procedures, as the heat generated during instrument operation can be detrimental to teeth.[4], [9], [10] DCU-supplied water is also used for oral rinsing by patients during and following dental treatment and to wash out the DCU spittoon, or cuspidor, after oral rinsing. DCUs supply water as a coolant and irrigant to turbine and conventional handpieces, ultrasonic scalers, three-in-one air/water syringes, as well as providing water for the patient rinse cup filler and cuspidor via an intricate network of interconnected narrow-bore tubes called dental unit waterlines (DUWs).[7], [8]

Over the last 20 years many studies have shown that water from DUWs is often contaminated with high densities of microorganisms, predominantly bacterial species.[7], [8], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23] This is a universal problem and all untreated DUWs in standard DCUs are subject to contamination and will host resident biofilms. Microbial contamination of DUWs originates predominantly in the DCU water supply, which usually contains low levels of microorganisms.[15], [22] In a typical modern DCU the waterline distribution network consists of several meters of plastic DUW tubing with an internal diameter of a few millimeters in which water can stagnate when the equipment is not being used.[16], [18] Microorganisms in water supplied to DCUs, predominantly aerobic heterotrophic Gram-negative environmental bacteria, attach to the internal surfaces of the DUW tubing and form microcolonies that eventually give rise to multispecies biofilm.[17], [20], [22] DUW biofilms are composed mainly of highly hydrated bacterial exopolysaccharide secreted by bacteria that contain microcolonies and single cells interspersed heterogeneously with channels or pores.[23], [24] Biofilm primarily forms in DUWs because water at the internal surface of the narrow-bore waterline tubing flows more slowly than water at the centre and thus there is little disturbance to any microorganisms present.16 This permits the microorganisms to multiply and subsequently disperse through the water supply as planktonic forms where they may be deposited at other sites within the waterline network or are transferred directly into the mouths of patients during dental procedures. For these reasons DUW biofilm acts as a reservoir for continuing contamination of DCU output water. Fig. 1, panels (a) and (b) show examples of biofilm in DUWs. Sterilisation of the handpieces, syringes and associated instruments makes no impact on biofilm within DUWs whatsoever.

The occurrence of high densities of microorganisms in DCU output water (up to 106 cfu/mL has been reported) constitutes a potential risk of infection for dental patients and dental healthcare and support staff and is diametrically opposed to good infection control practices.[14], [22], [25] Furthermore, it is ethically unacceptable to knowingly expose patients, dental healthcare staff and support staff to heavily contaminated water even if the assessable cross-infection risk is considered to be low. Previous studies have shown that bacteria in DCU output water are aerosolised by DCU handpieces during dental procedures and that dental personnel and patients are exposed to these microorganisms, to fragments of DUW-derived biofilm and to waterborne bacterial endotoxin, the latter consisting of lipopolysaccharide released from the cell walls of dead Gram-negative bacteria.[13], [26], [27], [28], [29], [30] Most of the bacterial species found in DCU output water are Gram-negative aerobic heterotrophic environmental bacterial species that exhibit very low pathogenicity although they may be of concern in the treatment of vulnerable patients, such as immunocompromised and medically compromised individuals.[7], [17], [20], [22] Nonetheless there is considerable potential for infection with some bacterial pathogens found in DCU output water such as Pseudomonas aeruginosa, Legionella pneumophila and non-tuberculosis Mycobacterium species.[13], [27], [29], [31] Only a few instances of cross-infection related to DUWs and associated biofilm have been reported in the literature.[13], [29] However, it is still possible that DCU output water-associated infections have gone undetected or unreported because of the failure to associate exposure to DCU output water and aerosols generated from this water with the development of specific infections. Sporadic infections not requiring hospital admission are also less likely to be investigated.

Section snippets

Water quality standards

According to the EU Medical Devices Directive “the devices and manufacturing processes must be designed in such a way as to eliminate or reduce as far as possible the risk of infection to the patient, user and third parties”.1 Thus DCU manufacturers have an important responsibility to design for reduced risk of biofilms and also to provide detailed and specific instructions in relation to control of DUW biofilm in the DCUs they manufacture and market to dental clinics and dental practitioners.

Biofilm control in DUWs

As mentioned above, until recently, responsibility for dealing with the problem of biofilm in DUWs has been considered the duty of the dental practitioner. DCU manufacturers have been slow to respond to the obvious need for DCU engineering and design changes to control DUW biofilms. Over the last 20 years numerous proposals, both chemical based and non-chemical based, for reducing the bacterial density in DCU output water have been suggested but none has been universally adopted that is both

Conclusions

Despite the increasing complexity and sophistication of DCUs, some of the fundamental issues concerning cross-infection control and biofilm establishment in DUWs have not yet been satisfactorily resolved. These difficulties arise from a number of quarters. First, there is no universally agreed standard for the quality of output water from a DCU and, in fact, there is often no specification regarding the quality of water supplied to the DCU either. These are clearly matters for the attention of

Acknowledgements

Research and development on DUW biofilm control systems and the development of solutions to DUW disinfection failure undertaken in the authors’ laboratory was supported by the Dublin Dental Hospital Board and the Microbiology Research Unit, Dublin Dental School & Hospital. We thank Declan Clarke from the Dublin Dental Hospital Building's Department for technical assistance with the DCUs. We especially wish to thank Jari-Pekka Teravainen, Tiina Sydanlammi, Kaisu Ilomaki, Anu Matilainen and Elina

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      This result is consistent with previous studies which demonstrated the microorganisms ranging from 102 to 108 CFU/ml [18–21]. Although some studies pointed out that tube diameters, water flow rates and service life of DCU may have influence on water quality in DUWLs [7,22–23], there was no significant difference among DCUs in terms of different departments, brands or service lives in the present studies. However, Barbeau et al. noted that just 4% or less microbial communities can be cultured from DUWLs [4].

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